Seyoon Gong

North Korea's leader Kim Jong-un has visited a shipyard at an undisclosed location to inspect the submarine under construction, the country's state media reported.

The Korean Central News Agency revealed also for the first time that the submarine is 8,700-ton class.

North Korea first publicized its plan for building nuclear subs in 2021 as part of a five-year military plan.

South Korea won President Trump's approval for acquiring nuclear subs in October.

It plans to hold working-level talks with the U.S.

starting early next year.

Kim Jong-un criticized Seoul's move as, quote, an offensive act that must be countered.

Seyoon Gong, NPR News, Seoul.